MADE EASY TEST SERIES

Question

Match List-I with List-II and select the correct answer using the codes given below the lists:

List-I	List-II
A. Stop and Wait ARQ	1. Each frame sent or resent needs a timer, which means that the timer needs to be numbered.
B. Go-back N ARQ	2. Ack all sent when data are delivered to network layer. It might be the case that, a single Ack acknowledges n frames.
C. Selective repeat ARQ	3. Only 2 sequence number used and sender window size is 1.
	4. No action performed by the received till the desired frame is obtained.

Codes:

	A	B	C
(a)	3	1	2
(b)	3	2	1
(c)	3	4	1
(d)	2	1	4

Below given snapshot is the solution provided by Made easy. Please point out the errors if any.

Comments

there reasoning is wrong but answer is correct

it could be b too but given the choice between b and c I would choose c too

Answer 1

GO BACK N: The receiver process keeps track of the sequence number of the next frame it expects to receive,

and sends that number with every ACK it sends.

The receiver will discard any frame that does not have the exact sequence number it expects (either a duplicate frame it already acknowledged, or an out-of-order frame it expects to receive later) and will resend an ACK for the last correct in-order frame.

^[1] Once the sender has sent all of the frames in its window, it will detect that all of the frames since the first lost frame are outstanding, and will go back to the sequence number of the last ACK it received from the receiver process and fill its window starting with that frame and continue the process over again.

Hence we can't say that no action is performed by receiving damaged or out of order frame

I think answer should be B

FOR A: 4 IS CORRECT

FOR C: '1' is COORECT, SELECTIVE REPEAT WE NEED SORTING which can be done through numbering of timer as it accepts out of order frames also

FOR B: 2 should be the answer which is nothing but CUMULATIVE ACK used by GO BACK N

Comments

what is numbering of timer??

and in these protocols,reciever send the acknowledgment for packets it has revieved,asking the sender to send the next packet.so it frame 1 is  sent,it will send ack 1,but u wrote it will send the ack number with byte expected next.thats des not happen in GO-back N.we do this in TCP.

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So what is the correct answer according to you Akriti ? Are those points mentioned in Made easy solution with reference to Selctive Repeat and GBN correct? Please guide me.

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according to me also,B is the correct answer

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answer can be both b and c but c seems more accurate